For anybody who finds this problem, the fix is to add the following line to the bundleconfig.cs file:
This will prevent the unobtrusive ajax script from loading twice (i.e. the minified and non-minified) in debug mode, which is what causes the double postback.
Alternatively, just remove the non minified script from the project (this obviously has implications for debugging, if you're inclined to debug the scripts included in the project template).
Telerik - this ought to be included in your how-to guide.